Method for the preparation of films containing radioactive materials and mounted on carriers



Dec. 30, 1969 w, EYR|H 3,486,935

METHOD FOR THE PREPARATION OF FILMS CONTAINING RADIOACTIVE MATERIALS AND MOUNTED 0N CARRIERS Filed Sept. 29, 1966 l//// 1 I Y/////// INVtWTa? KARL WERNER EYRZCH r WA/MW e P -q.

ATTORNEy5 United States Patent G Int. Cl. B44d 00:] /:02; B05c 7/00 US. Cl. 117-220 7 Claims The invention relates to a method for the preparation of films containing radioactive materials and mounted on carriers, especially for the preparation of a solid film containing a radioactive gas. The invention primarily relates to a method for the preparation of tritium targets.

The preparation of films containing radioactive materials, especially tritium targets, raises considerable difficulties because of the contamination hazard by the radioactive substances andconsequently-requires often comparatively awkward procedures. Tritium targets, for example, which essentially consist of a copper carrier, of a titanium film and of tritium bound by absorption in the titanium, are produced as follows: first the copper carrier is dampened with titanium in vacuum, thus forming the carrier film for tritium, then the titanium film and the carrier are exposed to air and finally loaded with tritium in a second apparatus. This second apparatus is necessary to avoid that the titanium films evaporated into the components of the damping apparatus, are not equally loaded with tritium and are, consequently, becoming contaminated by radioactivity. However, by exposing the titanium film to air, this latter is absorbing gases that have to be removed in the second apparatus. In most cases, they are not completely removable so that comparatively bad targets are obtained, i.e., targets whose tritium absorption is poor and which give off tritium during operation very easily, thus getting useless after a short period.

The task of this invention consists in developing a method for the preparation of films containing radioactive materials and mounted on carriers-especially for the pre aration of tritium targetsaccording to which one single apparatus is required for the process and a contamination of the apparatus components can, nevertheless, be practically avoided.

With the present invention this requirement is most easily achieved by manufacturing a practically hollow carrier, on the inner walls of which the'film is mounted. According to this method it is even possible to prepare films that are exclusively composed of radioactive materials, in a very simple manner, i.e., by evaporating the film material containing the radioactive substance or consisting of it in the interior of the cavity. The method according to the invention is particularly appropriate for the preparation of a solid film containing a radioactive gas. According to the invention the solid film is first prepared by evaporating in the interior of the cavity the material making up the solid film and then feeding the radioactive gas into the cavity to be subsequently absorbed by the solid film. It will be advantageous to evacuate by wellknown procedures at least the interior of the hollow carrier before evaporating the material making up the solid film. After the formation of the solid film the radioactive gas is fed into the evacuated cavity.

It is particularly advantageous that the material making up the film is brought into the cavity in a predetermined quantity which corresponds to the film thickness to be achieved, and that it is completely evaporated in the cavity.

According to the invention another advantageous method for the preparation of a solid film containing a radioactive gas, consists in preparing the film by cathode sputtering in a gaseous discharge which is mainly formed by ions of the radioactive gas. By this means, the storage of the radioactive gas is effected simultaneously to the formation of the solid film and the gas will be comparatively well bound.

The method covered by the invention will be explained in more detail below with the help of the attached figure. However, the specifications contained in it shall not constitute any limitation of the invention. Taking into consideration the instructions above, one rather can successfully apply the method in a modified form.

The copper-plate carrier 1 on which the film containing the radiocative material shall be mounted-in this case a titanium film to be loaded with tritium-is manufactured as a cylindrical case with an opening 2. Several evaporation rods 3 extend into the opening 2. The evaporation rods consist of tungsten covered by titaniumand tungsten Wire. The whole unit is located in a container 4 which is evacuated at the start of the process. First of all the carrier 1 is heated by a surrounding heating basket 5 whereby the carriers surface is cleaned. Then the evaporation rods 3 are heated to reach the volatilization temperature of titanium, thereby producing a titanium film of some 0.1l0 ,am. thickness on the inner surface of the cavity formed by the carrier 1. During the damping process the temperature of the carrier 1 is maintained through the heating basket 5 at some 450 C. On completion of titanium evaporation into the cavitys surface, i.e., when a predetermined film thickness is obtained on the carrier 1, the temperature of the evaporation rods 3 is reduced. The film thickness may be advantageously predetermined in such a way that only those quantities of titanium are deposited on the evaporation rods as are necessary for the preparation of the film. This results in the case of the invented method for the preparation of tritium targets in the important advantage that no tritium can be absorbed on the evaporation rods. In this case if there is any tritium left on the evaporation rods, the temperature during loading the titanium film on the carrier shall be maintained at such a level that tritium cannot be absorbed by the residues of titanium left on the rods. The container is thereupon separated from the evacuation machine, e.g., through valve 6, and tritium is fed into the evacuated container through valve 7. The temperature of the carrier is slowly reduced and the titanium film of the carrier is simultaneously loaded with tritum. The excessive tritium having been pumped out of the container 1, the latter can be ventilated and the carrier can be lifted out. True-tosize targets may be cut out of this carrier by punching out, cutting up, etc.

It has turned out in the preparation of tritium targets that at higher temperatures an addition of tungsten to the titanium film guarantees a better fixing of tritium in this film.

Apart from the simplicity and the aforementioned advantages of the method according to the invention which consist in practically avoiding a contamination of the apparatus used for preparation, a very homogeneous thickness of the film is achieved.

I claim:

1. A method for the preparation of a solid film containing a radioactive gas, said method comprising inserting into a vacuum chamber a generally cylindrical carrier for receiving a film deposit of a metal capable of absorbing said radioactive gas, depositing said metal film on the inside surface of said carrier by vacuum evaporation techniques, feeding said radioactive gas into said vacuum chamber and in contact with said film whereby said metal films becomes saturated with said radioactive gas and removing the remainder of the radioactive gas which is not absorbed in the metal film.

2. Method according to claim 1, characterized by the fact that the material making up the film is introduced in a predetermined quantitycorresponding to the film thicknessinto the cavity and is practically completely evaporated there.

3. Method according to claim 1, characterized by the fact that at least the interior of the hollow carrier is evacuated before vaporizing the material which makes up the solid film.

4. Method according to claim 1, characterized by the feeding of the radioactive gas into the cavity after the formation of the solid film.

5. Method according to claim 1, characterized by the fact that the solid film is made of titanium.

6. Method according to claim 1, characterized by the 15 fact that the solid film is made of titanium with an addition of tungsten.

7. Method according to claim 1, characterized by the fact that tritium is used as radioactive gas.

References Cited UNITED STATES PATENTS 2,847,331 8/1958 Ashley 117-220 3,380,853 4/1968 De Angelis 117220 FOREIGN PATENTS 234,233 6/1964 Austria.

ROBERT K. MIHALEK, Primary Examiner US. Cl. X.R. 

1. A METHOD FOR THE PREPARATION OF A SOLID FILM CONTAINING A RADIOACTIVE GAS, SAID METHOD COMPRISING INSERTING INTO A VACUM CHAMBER A GENERALLY CYLINDRICAL CARRIER FOR RECEIVING A FILM DEPOSIT OF A METAL CAPABLE OF ABSORBING SAID RADIOACTIVE GAS, DEPOSITING SAID METAL FILM ON THE INSIDE SURFACE OF SAID CARRIER BY VACUUM EVAPORATION TECHNIQUES, FEEDING SAID RADIOACTIVE GAS INTO SAID VACUUM CHAMBER AND IN CONTACT WITH SAID FILM WHEREBY SAID METAL FILMS BECOMES SATURATED WITH SAID RADIOACTIVE GAS AND REMOVING THE REMAINDER OF THE RADIOACTIVE GAS WHICH IS NOT ABSORBED IN THE METAL FILM. 